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Re: Cheap electret microphones for environmental noise measurements

Subject: Re: Cheap electret microphones for environmental noise measurements
From: "Eric Benjamin" ericbenjamin2
Date: Thu Jun 26, 2014 10:08 am ((PDT))
OK. =C2=A0That gives me a better idea of how the system is configured. =C2=
=A0It sounds as though you already have the radio and microcontroller parts=
 fairly worked out. =C2=A0As I see it, the system consists of a (waterproof=
) enclosure, a microphone and associated preamplifier, microcontroller, rad=
io, and a battery to power it all. =C2=A0You are monitoring noise so high f=
requency response of the microphones is not a great issue. =C2=A0Are you us=
ing A-weighting? =C2=A0

I'm envisioning these motes as needing to be rugged, so something like the =
Hammond diecast aluminum enclosures. =C2=A0They have weather resistant ones=
, and waterproof with O-rings. =C2=A0But the main problem is that you need =
to get signals into and out of the box! =C2=A0At least the microphone signa=
l and the radio antenna. =C2=A0You will need to work out how to waterproof =
those junctions. =C2=A0I envision a small tube with the microphone capsule =
mounted in the end, protruding through a grommet sealed to the enclosure.

How long does the battery need to last? =C2=A0Is microphone supply current,=
 at ~0.5 mA for typical electrets and less than 50 uA for hearing aid types=
, constitute a significant problem?

On Thursday, June 26, 2014 2:39 AM, " [naturerecordists]=
" <> wrote:

Thanks a lot for your quick and useful response, those microphone capsules =
from Knowles look really interesting!

I already found the micbuilders group, but sent the request to join it two =
days ago and I have yet to receive a reply.

About the number of systems (let's call them "motes") I need to build, I do=
n't have yet the exact number, but maybe they will be 50 or more. I'd like =
each one to cost less than 100=E2=82=AC if possible. They will be equipped =
with a microphone, a temperature (and maybe also humidity) sensor, a microc=
ontroller and an IEEE 802.15.4 radio interface.

About the radio link, let me detail how it will be used a bit more: microph=
one raw data will not be sent through the audio interface, it will be proce=
ssed locally by each mote (to compute sound pressure levels, etc), and only=
 results will be sent. I'm avoiding cables because I will use a relatively =
high number of motes and they will be far of each one. Communicating them a=
ll via cable would be difficult.

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